Recent trends in manufacturing of electronic equipment place increased emphasis on reliability and robustness of components employed in such equipment. Effective heat dissipation for power devices pose particular problems for several reasons. Typically, photolithographically defined structures on a top surface of a semiconductor device generate heat while thermally conductive attachment to a heatsink is effected via a bottom surface thereof. Heat thus is coupled from the active device area, through the die and then to the heatsink. As integration levels increase, larger amounts of heat are generated at the top surface and coupled through semiconductor materials having relatively poor thermal conductivity and heat capacity, which can determine the maximum packing density of large scale integrated circuits and/or large-signal or power semiconductor devices. Devices atop the die surface which are not necessarily generating heat themselves are heated by nearby structures, affecting the electronic properties thereof.
One approach to heat removal which has been attempted is to place the semiconductor device in a specially designed liquid-containing device package and lid. A dielectric liquid having benign chemical properties and suitable thermal properties (e.g., vaporization and solidification temperatures) is employed. Prior art packages employ heat exchanging structures and/or bellows to accommodate the liquid-containing cavity and to allow for thermal expansion, etc. These arrangements are not cost-effective for many microelectronic packaging applications. Furthermore, techniques developed to date for evacuating the cavity and back-filling same with dielectric liquids are complex, labor-intensive and poorly suited to volume production. Moreover, approaches employing large cavities and relatively small volumes of liquid therein are not able to maintain the liquid in contact with the chip area absent gravity, in the presence of some accelerations and/or unless the package is in a particular position, which tends to limit the applications for which such packages are well suited.
What are needed are methods and apparatus for providing liquid-filled or liquid-containing semiconductor device packages which also provide improved manufacturability and which are suited to a broad range of applications.